/*
 * pgp-mpi-openssl.c
 *	  OpenPGP MPI functions using OpenSSL BIGNUM code.
 *
 * Copyright (c) 2005 Marko Kreen
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *	  notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *	  notice, this list of conditions and the following disclaimer in the
 *	  documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.	IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * contrib/pgcrypto/pgp-mpi-openssl.c
 */
#include "postgres.h"
#include "knl/knl_variable.h"

#include <openssl/bn.h>

#include "px.h"
#include "mbuf.h"
#include "pgp.h"

static BIGNUM* mpi_to_bn(PGP_MPI* n)
{
    BIGNUM* bn = BN_bin2bn(n->data, n->bytes, NULL);

    if (!bn)
        return NULL;
    if (BN_num_bits(bn) != n->bits) {
        px_debug("mpi_to_bn: bignum conversion failed: mpi=%d, bn=%d", n->bits, BN_num_bits(bn));
        BN_clear_free(bn);
        return NULL;
    }
    return bn;
}

static PGP_MPI* bn_to_mpi(BIGNUM* bn)
{
    int res;
    PGP_MPI* n = NULL;

    res = pgp_mpi_alloc(BN_num_bits(bn), &n);
    if (res < 0)
        return NULL;

    if (BN_num_bytes(bn) != n->bytes) {
        px_debug("bn_to_mpi: bignum conversion failed: bn=%d, mpi=%d", BN_num_bytes(bn), n->bytes);
        pgp_mpi_free(n);
        return NULL;
    }
    BN_bn2bin(bn, n->data);
    return n;
}

/*
 * Decide the number of bits in the random componont k
 *
 * It should be in the same range as p for signing (which
 * is deprecated), but can be much smaller for encrypting.
 *
 * Until I research it further, I just mimic gpg behaviour.
 * It has a special mapping table, for values <= 5120,
 * above that it uses 'arbitrary high number'.	Following
 * algorihm hovers 10-70 bits above gpg values.  And for
 * larger p, it uses gpg's algorihm.
 *
 * The point is - if k gets large, encryption will be
 * really slow.  It does not matter for decryption.
 */
static int decide_k_bits(int p_bits)
{
    if (p_bits <= 5120)
        return p_bits / 10 + 160;
    else
        return (p_bits / 8 + 200) * 3 / 2;
}

int pgp_elgamal_encrypt(PGP_PubKey* pk, PGP_MPI* _m, PGP_MPI** c1_p, PGP_MPI** c2_p)
{
    int res = PXE_PGP_MATH_FAILED;
    int k_bits;
    BIGNUM* m = mpi_to_bn(_m);
    BIGNUM* p = mpi_to_bn(pk->pub.elg.p);
    BIGNUM* g = mpi_to_bn(pk->pub.elg.g);
    BIGNUM* y = mpi_to_bn(pk->pub.elg.y);
    BIGNUM* k = BN_new();
    BIGNUM* yk = BN_new();
    BIGNUM* c1 = BN_new();
    BIGNUM* c2 = BN_new();
    BN_CTX* tmp = BN_CTX_new();

    if (!m || !p || !g || !y || !k || !yk || !c1 || !c2 || !tmp)
        goto err;

    /*
     * generate k
     */
    k_bits = decide_k_bits(BN_num_bits(p));
    if (!BN_rand(k, k_bits, 0, 0))
        goto err;

    /*
     * c1 = g^k c2 = m * y^k
     */
    if (!BN_mod_exp(c1, g, k, p, tmp))
        goto err;
    if (!BN_mod_exp(yk, y, k, p, tmp))
        goto err;
    if (!BN_mod_mul(c2, m, yk, p, tmp))
        goto err;

    /* result */
    *c1_p = bn_to_mpi(c1);
    *c2_p = bn_to_mpi(c2);
    if (*c1_p && *c2_p)
        res = 0;
err:
    if (tmp)
        BN_CTX_free(tmp);
    if (c2)
        BN_clear_free(c2);
    if (c1)
        BN_clear_free(c1);
    if (yk)
        BN_clear_free(yk);
    if (k)
        BN_clear_free(k);
    if (y)
        BN_clear_free(y);
    if (g)
        BN_clear_free(g);
    if (p)
        BN_clear_free(p);
    if (m)
        BN_clear_free(m);
    return res;
}

int pgp_elgamal_decrypt(PGP_PubKey* pk, PGP_MPI* _c1, PGP_MPI* _c2, PGP_MPI** msg_p)
{
    int res = PXE_PGP_MATH_FAILED;
    BIGNUM* c1 = mpi_to_bn(_c1);
    BIGNUM* c2 = mpi_to_bn(_c2);
    BIGNUM* p = mpi_to_bn(pk->pub.elg.p);
    BIGNUM* x = mpi_to_bn(pk->sec.elg.x);
    BIGNUM* c1x = BN_new();
    BIGNUM* div = BN_new();
    BIGNUM* m = BN_new();
    BN_CTX* tmp = BN_CTX_new();

    if (!c1 || !c2 || !p || !x || !c1x || !div || !m || !tmp)
        goto err;

    /*
     * m = c2 / (c1^x)
     */
    if (!BN_mod_exp(c1x, c1, x, p, tmp))
        goto err;
    if (!BN_mod_inverse(div, c1x, p, tmp))
        goto err;
    if (!BN_mod_mul(m, c2, div, p, tmp))
        goto err;

    /* result */
    *msg_p = bn_to_mpi(m);
    if (*msg_p)
        res = 0;
err:
    if (tmp)
        BN_CTX_free(tmp);
    if (m)
        BN_clear_free(m);
    if (div)
        BN_clear_free(div);
    if (c1x)
        BN_clear_free(c1x);
    if (x)
        BN_clear_free(x);
    if (p)
        BN_clear_free(p);
    if (c2)
        BN_clear_free(c2);
    if (c1)
        BN_clear_free(c1);
    return res;
}

int pgp_rsa_encrypt(PGP_PubKey* pk, PGP_MPI* _m, PGP_MPI** c_p)
{
    int res = PXE_PGP_MATH_FAILED;
    BIGNUM* m = mpi_to_bn(_m);
    BIGNUM* e = mpi_to_bn(pk->pub.rsa.e);
    BIGNUM* n = mpi_to_bn(pk->pub.rsa.n);
    BIGNUM* c = BN_new();
    BN_CTX* tmp = BN_CTX_new();

    if (!m || !e || !n || !c || !tmp)
        goto err;

    /*
     * c = m ^ e
     */
    if (!BN_mod_exp(c, m, e, n, tmp))
        goto err;

    *c_p = bn_to_mpi(c);
    if (*c_p)
        res = 0;
err:
    if (tmp)
        BN_CTX_free(tmp);
    if (c)
        BN_clear_free(c);
    if (n)
        BN_clear_free(n);
    if (e)
        BN_clear_free(e);
    if (m)
        BN_clear_free(m);
    return res;
}

int pgp_rsa_decrypt(PGP_PubKey* pk, PGP_MPI* _c, PGP_MPI** m_p)
{
    int res = PXE_PGP_MATH_FAILED;
    BIGNUM* c = mpi_to_bn(_c);
    BIGNUM* d = mpi_to_bn(pk->sec.rsa.d);
    BIGNUM* n = mpi_to_bn(pk->pub.rsa.n);
    BIGNUM* m = BN_new();
    BN_CTX* tmp = BN_CTX_new();

    if (!m || !d || !n || !c || !tmp)
        goto err;

    /*
     * m = c ^ d
     */
    if (!BN_mod_exp(m, c, d, n, tmp))
        goto err;

    *m_p = bn_to_mpi(m);
    if (*m_p)
        res = 0;
err:
    if (tmp)
        BN_CTX_free(tmp);
    if (m)
        BN_clear_free(m);
    if (n)
        BN_clear_free(n);
    if (d)
        BN_clear_free(d);
    if (c)
        BN_clear_free(c);
    return res;
}
